1. Field of the Invention
The present invention relates to a network testing apparatus, a network testing method and a recording medium storing a network testing program for testing events occurring within a network installed between an OLT or an ONT and an ONU or the ONT and constructed by connecting one optical fiber between the OLT or the ONT and the ONU or the ONT.
2. Description of the Related Art
Hitherto, as one of technologies for realizing FTTH (Fiber To The Home) for transmitting optical signals transmitted from an accommodating station such as a common carrier to a plurality of subscriber's homes, PON (Passive Optical Network) for transmitting signals to the plurality of homes by splitting one optical fiber by a splitting device such as a splitter has been used. In the PON, an OLT (Optical Line Terminal) within the accommodating station and a plurality of ONU/ONT (Optical Network Unit/Optical Network Termination) are configured in a model of point-to-multi-points.
Lately, G-PON (Gigabit-passive Optical Networks) standardized by the ITU-T: Telecommunication-Standardization Sector, International Telecommunication Union) and that realizes a transmission speed of gigabits (Gbps) has come to be used. Because a transmission frame of the G-PON is set to be a fixed length frame of period of 125 microseconds that is the same period with a basic time unit of the conventional telecommunication services, it enables one to efficiently use existing services such as telephone and dedicated lines. For example, the G-PON can realize multi-channel broadcasting and access lines of 1 Gbps by putting communication and broadcasting into one optical fiber cable.
Then, in a G-PON type network structure as shown in FIG. 13, communication between a communication unit A, which is OLT or ONT, and communication units B1 through Bn, which are ONU and/or ONT, is in a relationship of 1:n. In order to prevent data (referred to as downstream data hereinafter) transmitted from the communication unit A from colliding with data (referred to as upstream data hereinafter) transmitted from the communication units B1 through Bn, the communication unit A continuously transmits the downstream data to the communication units B1 through Bn and the communication units B1 through Bn transmit the upstream data to the communication unit A in a time-division manner.
Specifically, the communication unit A measures communication time (Tb1 through Tbn) with the communication units B1 through Bn and instructs the communication units B1 through Bn to respond to the communication unit A corresponding to the measured time. Then, receiving the instruction, the communication units B1 through Bn transmit the upstream data by the specified time-division manner. It is noted that the series of processes described above is called as Ranging and the Ranging is always carried out once or more when the communication is physically established periodically or with a change of condition of the network as a momentum.
Because the communication between the communication unit A (OLT/ONT) and the communication units B1 through Bn (ONU/ONT) assumes the relationship of 1:n in the G-PON type network structure, it is essential for the communication units B1 through Bn to transmit the upstream data in the time-division manner. Still more, an occurrence of such collision of data may become a large trouble for a large-scale G-PON system in which a large number of communication units B (ONU/ONT) is connected to the communication unit A (OLT/ONT). Then, there have been disclosed various technologies for testing or verifying whether or not transmission/receiving of data between the communication unit A and the communication units B1 through Bn can be made correctly without collision by the Ranging described above.
For example, according to Patent Document 1 (JP Patent Application Laid-open No. 2005-20420), a testing apparatus for testing normal communication is composed of a standard OLT 1, an ONU-to-be-tested 2, a pseudo ONU 3 and a frame generator/tester 4 as shown in FIG. 14. The pseudo ONU 3 is an ONU that plays a pseudo role of simulating operations of a plurality of ONUs. When the frame generator/tester transmits data to the ONU-to-be-tested 2 in this structure, the ONU-to-be-tested 2 transmits the data to the standard OLT 1 with timing assigned (set) to the own unit. Then, the standard OLT 1 transmits the received data to the frame generator/tester 4 and the frame generator/tester 4 tests whether or not the data is transmitted with normal timing. The use of such testing apparatus allows the connected ONU to be tested one by one, the test of the complicated network to be readily carried out and troubles and problems to be readily detected as compared to a case of simultaneously testing all ONUs connected in the G-PON system.
However, the testing apparatus of Patent Document 1 described above merely tests only operations of the OLT and ONUs to the end and cannot test events occurring within the network, such as delayed insertion of input data, fluctuation or jitter of data arrival time, fall of part or all transmission data and reversal of sequence of data. When data arrival time to the ONU-to-be-tested 2 is late due to the event occurring within the network for example, the ONU-to-be-tested 2 cannot transmit data with timing (time-division) assigned to itself and may cause such a problem that data collision occurs between other ONUs and the OLT as a result. Therefore, it is necessary to test such events occurring within the network.
In general, a testing system in which testing apparatuses 1 through n and a testing apparatus 0 or a communication monitor are connected to the outside of the G-PON system (G-PON network) composed of a communication unit A (OLT/ONT) and communication units B1 through Bn (ONUs/ONTs) as shown in FIG. 15 is used. The testing apparatuses 0 through n used here are what test whether or not the units normally operate similarly to Patent Document 1 described above and the testing apparatus 0 tests events occurring within the network. When the communication monitor is used instead of the testing apparatus 0, the communication monitor detects the event occurring within the network by obtaining and analyzing data flowing within the G-PON system.
When the testing apparatus 0 is provided between the communication unit A (OLT/ONT) and the communication units B1 through Bn (ONUs/ONTs) in order to verify the event occurring within the network in the prior art technology described above, however, the data flowing within the G-PON system passes through the testing apparatus 0 and an error occurs in a data communication time within the system. Therefore, there has been a problem that data collision occurs even between the normally operating OLT and ONUs and that the testing apparatus 0 cannot test the event occurring within the network during the normal communication.
Specifically, all data within the G-PON system pass through the testing apparatus 0, fluctuating the communication time (Tb1 through Tbn) between the communication unit A and the communication units B1 through Bn. That is, when a test is being implemented between the communication unit A and the communication unit B1, the communication time between the communication unit A and the communication unit B1 fluctuates even though the communication is being normally implemented between the communication unit A and the communication unit B1 through Bn, causing such an event that data transmitted from the communication unit B1 collides against data transmitted from the communication unit B2. Therefore, the testing apparatus 0 cannot test the event occurring within the network in the normal communication.
The prior art technology described above has also had a problem that it requires an enormous amount of time because it obtains contents and result of test by obtaining and analyzing an enormous amount of data flowing within the G-PON system in testing the events occurring within the network.